The present invention relates to a rectifier circuit and, more particularly, to a circuit for converting an A.C. electrical power signal to a D.C. electrical power signal, in which the waveshape of the A.C. power signal is not distorted by the rectification process.
Rectifier circuits which provide a source of D.C. electrical power are known in which a transformer has its primary winding connected to an A.C. electrical power signal source and a secondary winding connected in series with a diode and a storage capacity. In this arrangement, the diode is forward biased during alternate half cycles so as to charge the capacitor to the potential of the secondary winding. If desired, additional diodes may be connected in a full-wave rectifier bridge so as to apply a charging potential to the capacitor during both positive and negative half cycles of the A.C. signal. Rectified D.C. power is available across the capacitor, which provides a smoothing action.
It will be appreciated that the capacitor will receive charging currents only when the series connected diode is forward biased. During steady state operation, the A.C. voltage induced in the secondary winding will exceed the potential across the capacitor, and thereby forward bias the diode, only during a relatively short interval of each half cycle. As a consequence, the charging current to the capacitor will be of very short duration. This current spike in the secondary of the transformer produces a corresponding current spike in the primary winding, thus producing irregularities in the voltage waveform of the A.C. electrical power signal. This waveform distortion can have an adverse effect on the operation of other circuits connected to the same A.C. electrical power distribution system.
Further problems may occur where a number of single phase rectifiers are connected in a number of the phases of a multi-phase power system. The distorted voltage and current waveshapes have been found to produce a substantial net current flow through the neutral conductor of the power system. The currents produced by the separate phases of the system, rather than cancelling in the neutral conductor as would normally be the case, can instead add together to produce a neutral current flow which is in excess of the rated current-handling capabilities of the neutral conductor. Further, this current through the neutral conductor is at a frequency equal to three times the frequency of the A.C. power signal. This high frequency current increases the heat loss produced in the transformer core of the polyphase transformer of the power system.
It is seen, therefore, that a need exists for a rectifier device for converting an A.C. power signal into a D.C. power signal in which minimal waveshape distortion of the A.C. power signal is produced.